Temperature sensitive control wires provided with transistors for electrically heated pads, blankets and the like



Aug. 30, 1966 A. NEGROMANTI 3,270,184

TEMPERATURE SENSITIVE CONTROL WIRES PROVIDED WITH TRANSISTORS FOR ELECTRICALLY HEATED PADS, BLANKETS AND THE LIKE Filed Dec. 26, 1963 United States Patent 3,270,184 TEMPERATURE SENSITIVE CONTROL WIRES PRO- VIDED WITH TRANSISTORS FOR ELECTRICAL LY HEATED PADS, BLANKETS AND THE LIKE Antonio Negromanti, Via Fratelli Lorenzetti 6, Milan, Italy Filed Dec. 26, 1963, Ser. No. 333,388 Claims priority, application Great Britain, Jan. 9, 1963, 1,049/ 63 4 Claims. (Cl. 219501) The invention relates to temperature control means for electrically heated pads, blankets and the like.

In my British Patent No. 783,883 there is described and claimed an electrically heated fabric characterised by the feature that the resistance wiring of the heating circuit is wound around but electrically insulated from two wires which are in close contact with one another throughout their length but are insulated from one another by a substance which becomes a good conductor of electricity only at a predetermined critical temperature which it is desired not to exceed, but returns to a non-conducting state as soon as the temperature returns to its normal value, these wires forming part of the excitation circuit of a relay, which, when excited, interrupts the heating circuit temporarily.

Substances capable of making this reversal an indefinite number of times are known, both among inorganic substances (for instance certain metal oxides) and among organic ones (for instance certain synthetic polyamid resins).

In other words the two metallic control conductors are insulated from one another by a composition having a high negative thermal co-efficient of resistance.

The arrangement above referred to has the disadvantage that the number of substances having a negative co-efiicient of resistance with change of temperature which can be used is small, and they do not become suificiently good conductors until the temperature is in the neighbourhood of 100 C.

The object of the present invention is to provide control means of the kind here above described for electrically heated pads, blankets and the like which do not have the disadvantages above mentioned and which allows the choice of substances from a far greater range and to give a closer control of temperature than before.

The invention consists in a temperature control means for electrically heated pads, blankets and the like as above described, characterised in having a circuit including one or more transistors which amplify the current passing through the sensitive material as a result of its increasing in temperature above the normal one.

The invention further consists in a temperature control means as set forth in the preceding paragraph in which the electric circuit includes a manually variable resistor by means of which the temperature of the blanket or the like is adjustable.

The invention still further consists in a temperature control means as set forth above in which the electric circuit includes a relay which is operated to open the heating circuit of the blanket or the like when the current through the transistor rises above a predetermined maximum value.

Moreover, the invention provides for the employment of a thermistor in the circuit of the relay to re-establish connection after a time lag, in order to maintain the temperature of the pad, blanket or the like, substantially constant.

The accompanying drawing shows, by way of example only, one embodiment of the invention and comprises a transformer having a primary 1 suitable for use with the main domestic supply and a secondary 2 providing,

3,270,184 Patented August 30, 1966 for example, a low voltage of 22 volts. The output of the secondary of the transformer is rectified by the full wave rectifier 3 and the current is smoothed by the electrolytic capacitor 4.

The diodes 5 and 6 are connected by their cathodes to the emitter and collector respectively of the transistor 7, while the coil 8 of a relay is connected in parallel with the diode 6. The resistors 9 and 10, which may be of 5,000 ohms and 5,600 ohms respectively, form part of a bridge circuit, the point of junction of which is connected to the base of the transistor.

The heating wires 11 of the pad or blanket or the like, shown here in the form of a helix, are connected in series with the contacts 12 and 13 of the relay and are fed by current to the connectors 14. When the relay is energised the circuit is closed and the heating wires pass current.

The temperature responsive element comprises a pair of parallel wires '15 and 16 which are separated from one another by thermal sensitive material 17. The wires 15 and 16 are connected to the ends of the resistor 9 in series with the adjustable resistor 18.

By means of the adjustable resistor 18 the shunting effect of the temperature responsive element can be adjusted to give the effect required. The values of the resistors 9. and 10 are so chosen that as soon as current is supplied to the transformer the relay is energised and the heating Wires 11 begin to get hot. When a temperature is reached as will cause the shunting resistance of the material 17 in conjunction with resistor 18 to fall to a predetermined value, the current in the bridge is changed and the contacts of the relay open and the current of the heating wires 11 is interrupted. When the temperature has fallen to a value as will cause the relay contacts to close the current is restored to the heating wires 11. By this means a substantially constant temperature is maintained in the pad or blanket.

For example, if when the variable resistor is in the position of no resistance, and the resistance of the sensitive material 17, at the temperature of 30 C., falls to a value of 200 ohms, for the values of the resistors given, the relay contacts '12 and 13 are open and the heating current is interrupted. The consequent cooling of the pad Or blanket causes the material 17 to increase its resistance and the relay contacts again close.

If now the value of the adjustable resistor 18 is increased it is clear that in order to cause the contacts of the relay to open it is necessary for the resistance of the material 17 to fall to a lower value than before, for which purpose the material must reach a temperature higher than 30 C.

As there is between the wires 15 and 16, 22 volts only, a negligible current passes as the temperature of 30 C. is reached. Nevertheless, such cur-rent is amplified by the transistor 7 and the relay is de-energised.

It can be appreciated that in each position of the adjustable resistor 18 there is a corresponding temperature of the blanket.

The wires 15 and 16 and the sensing material 17 are in the embodiment mentioned enclosed in the helix of the heating wire 11 and insulated therefrom, and consequently even if the blanket is inadvertently supplied with current when folded several times the sensing means will quickly be brought to a temperature which corresponds to a sufficiently low resistance to cause the relay contacts 12 and 13 to open.

However, the sensitive material can be warmed also indirectly. In such a case the heating wire 11 is wound apart, on a core of insulating material, for instance of cotton, and the temperature control means may be distributed, if desired, only in some preferred zones of the blanket or the like.

J As already said, the embodiment of the invention shown in the accompanying drawings is by way of example only.

So, instead of a bridge circuit, it is possible to employ circuits of other kinds without departing from the scope and spirit of the invention which is that of amplifying, by mean-s of one or more transistors, the current which takes place through the sensing material in consequence of its increasing in temperature .above the normal one.

Also, the two wires and 16 can be disposed in a different manner from that shown in the drawing, for in stance both may be coiled on a core of sensible material but separated from one another by said material.

:I claim:

1. An electronically controlled electrically heated blanket operable from a mains voltage source comprising a heating element adapted to be operated at mains voltage, a heat sensor comprising a pair of wires positioned in close proximity to one another throughout their length; a heat sensitive electrical conductor of relatively high electrical resistance at normal room temperatures in comparison with the resistance of said wires embedding the wires, and of negative co-efficient of electrical resistance, the heat sensor being substantially the same length as, and located .at least in close proximity to the heating element throughout its length, a relay having contacts which are in circuit with the heating element, a source of DC. potential of approximately 22 volts; and a transistor amplifier the input of which is connected to the pair of wires and the source of DC. potential and the output of which is connected to the relay, the circuit connected to the DC. source being electrically isolated from the circuit of the heating element.

2. An electronically controlled electrically heated blanket operable from a mains voltage source comprising a heating element in the configuration of a helix and adapted to be operated at mains voltage; a heat sensor comprising a pair of wires positioned in close proximityof DC. potential may be connected; and a transistor amplifier having input terminals connected to the pair of wires and the terminals of the source of DC. potential; said amplifier having an output which is connected to the relay, the circuit at the DC. potential being electrically isolated from the circuit of the heating element.

3. An electronically controlled electrically heated blanket for operation from an AC. main voltage source comprising a heating element in the form of a helix and adapted to be operated at main voltage, .a heat sensor comprising a pair of wires positioned in close proximity to one another and of uniform distance apart throughout their length and embedded in a rod-like heat sensitive electrical conductor of relatively high electrical resistance at normal room temperatures and of negative co-efficient of electrical resistance, the helix of the heating element being wound upon the rod-like conductor, the heat sensor being substantially of the same length as the heating element, an electromagnetic relay the contacts of which are in the circuit of the heating element, a source of DC. potential in the region of 22 volts, a Wheatstone bridge circuit, the pair of wires being connected in series with a manually variable resistor as a shunt in one arm of the wheatstone bridge, and a transistor amplifier the input of which is connected between opposite junctions of the bridge and the output of which is connected to the energising coil of the relay.

4. Heating and temperature control means as claimed in claim 1 in which a thermistor is connected in series with the contacts of the relay to delay the :re-establi-shrnent of the full heating current each time the circuit of the heating element is completed to limit the frequency of interruption of the element circuit.

References Cited by the Examiner UNITED STATES PATENTS 3,051,815 8/1962 Hukee et al. 2l9501 3,068,338 12/1962 Bigler 2l9501 3,107,285 10/1963 Knapp 219-501 FOREIGN PATENTS 783,883 10/1957 Great Britain.

RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner.

L. H. BENDER, Assistant Examiner. 

1. AN ELECTRONICALLY CONTROLLD ELECTRICALLY HEATED BLANKET OPERABLE FROM A MAINS VOLTAGE SOURCE COMPRISING A HEATING ELEMENT ADAPTED TO BE OPERATED AT MAINS VOLTAGE, A HEAT SENSOR COMPRISING A PAIR OF WIRES POSITIONED IN CLOSE PROXIMITY TO ONE ANOTHER THROUGHOUT THEIR LENGTH; A HEAT SENSITIVE ELECTRICAL CONDUCTOR OF RELATIVELY HIGH ELECTRICAL RESISTANCE AT NORMAL ROOM TEMPERTURES IN COMPARISON WITH THE RESISTANCE OF SAID WIRES EMBEDDING THE WIRES, AND OF NEGATIVE CO-EFFICIENT OF ELECTRICAL RESISTANCE, THE HEAT SENSOR BEING SUBSTANTIALLY THE SAME LENGTH AS, AND LOCATED AT LEAST IN CLOSE PROXIMITY TO THE HEATING ELEMENT THROUGHOUT ITS LENGTH, A RELAY HAVING CONTACTS WHICH ARE IN CIRCUIT WITH THE HEATING ELEMENT, A SOURCE OF D.C. POTENTIAL OF APPROXIMATELY 22 VOLTS; AND A TRANSISTOR AMPLIFIER THE INPUT OF WHICH IS CONNECTED TO THE PAIR OF WIRES AND THE SOURCE OF D.C. POTENTIAL AND THE OUTPUT OF WHICH IS CONNECTED TO THE RELAY, THE CIRCUIT CONNECTED TO THE D.C. SOURCE BEING ELECTRICALLY ISOLATED FROM THE CIRCUIT OF THE HEATING ELEMENT. 